A next generation communication system aims at providing high rate data transmission, high spectrum utilization and large system capacity. The MIMO technique has been focused on and researched for several years, since it proved to be capable of improving the data transmission rate and system capacity dramatically. However, in a multi-user MIMO system, since techniques of joint detection, spatial code, etc. could not be used together with user terminals because antennas between different users are independent from each other, it is needed to transfer information about channel characteristics acquired by each terminal to the network, so that techniques, such as the multi-user interference technique, could be further adopted in base stations.
However, in practice, since the bandwidth of a feedback channel between a terminal and a base station is limited and thus limits the amount of feedback information, there is a need for a method such that, in the case of limited feedback and user selection diversity, the base station could acquire exact information on channel characteristics etc. known by each terminal, thus enabling, for different channel characteristics of different users, to improve the data transmission rate and system capacity etc. through optimizing the selection of pre-coding vectors.
For optimizing the selection of pre-coding vectors, a method for per-user unitary rate control (PU2RC) has been proposed in a Patent Application with Serial No. EP1699145A2, entitled “Beam and power allocation method for MIMO communication system”, filed in March, 2006 by SAMSUNG Company. However, there is a limitation in PU2RC, i.e. that the pre-coding codebook used by a base station must be a unitary matrix, i.e., any two pre-coding vectors in the pre-coding codebook should be orthogonal to each other, so that the selection range of pre-coding vectors is limited, thus resulting in that the pre-coding codebook selected in most cases could only meet requirements of partial users for transmission rate and signal-noise ratio at the cost of other users' performance. Consequently, the total data transmission rate and total system capacity of the system as a whole are further limited.
Therefore, there is a need to propose a method that is capable of improving the total data transmission rate and total system capacity of a system through further optimizing the selection of pre-coding vectors.